The next time your dog greets you when you come home, closely watch his tail. Scientists have discovered that a happy dog will wag harder to the right and an anxious dog will wag harder to the left.

The study’s findings, “Asymmetric tail-wagging responses by dogs to different emotive stimuli,” was recently published in Current Biology. Co-authors include neuroscientist Giorgio Vallortigara of the University of Trieste in Italy, and veterinarians Angelo Quaranta and Marcello Siniscalchi, at the University of Bari in Italy.

In humans, it’s well documented that the brain is divided into two cerebral hemispheres—left and right—which serve different functions and control opposite sides of the body. Most animals also demonstrate a difference between “left brain” and “right brain” functions. It is believed that the left brain in animals specializes in “approach and energy enrichment,” such as finding food. The right brain specializes in “withdrawal and energy expenditure,” such as fleeing in response to fear. Because the dog’s tail is located along the body’s midline, researchers questioned whether or not the tail displayed emotional asymmetry.

Thirty mixed-breed dogs, family pets, served as the researchers’ subjects. Each dog was put in a cage specially fitted with cameras to capture the precise angle of the dog’s tail movement. The dog was then shown four separate stimuli—his owner; a stranger; a friendly cat; and an unfamiliar, intimidating dog—for one minute each.

Upon sight of their owners, all 30 dogs wagged their tails more strongly to the right side. After a 90-second rest period, the dogs viewed a stranger. The dogs’ tails still favored the right side, but the angle was more moderate in comparison to seeing their owner. The cat elicited a bias to the right side, but it was even more subtle than when they saw the stranger. The large, unknown dog caused all of the dogs to wag their tails to more to the left.

The authors concluded that when the dog felt positive, or curious (as in the case of the cat), the tail wagged right. If the dog felt negative or apprehensive, the tail wagged left. Since the left brain controls the right side of the body, the right muscles of the tail expressed those good feelings. The left muscles of the tail signaled caution or concern, which is controlled by the right brain.

It’s always a good idea to observe your dog’s body language, whether you’re relaxing at the dog park or waiting to see the vet. Now, thanks to your dog’s tail, you have another way to tell how he really feels.

Julia Kamysz Lane, owner of Spot On K9 Sports and contributing editor at The Bark, is the author of multiple New Orleans travel guides, including Frommer’sNew Orleans Day by Day (3rd Edition). Her work has also appeared in The New York Times Magazine, Poets and Writers and Publishers Weekly.